1. Field of the Invention
The present invention relates to a display device and method of fabricating a display device, and more particularly, to a liquid crystal display device and a method of fabricating a liquid crystal display device.
2. Description of the Related Art
In general, liquid crystal display (LCD) devices control light transmittance of liquid crystal cells arranged in a matrix configuration in response to video signals to display images corresponding to the video signals on liquid crystal display panels. The LCD device includes a liquid crystal display panel having liquid crystal cells arranged in an active matrix array, and driving integrated circuits (ICs) for driving the liquid crystal cells. The driving ICs are mounted on a tape carrier package (TCP) when they are manufacture by a tape automated bonding (TAB) system. Conversely, the driving ICs are mounted on a surface of the liquid crystal panel when they are manufactured by a chip-on-glass (COG) system. In the TAB system, the driving ICs are electrically connected to a pad portion provided in the liquid crystal panel by means of the TCP.
FIG. 1 is a plan view of a liquid crystal display device according to the related art, and FIG. 2 is a cross sectional view along II-II′ of FIG. 1 according to the related art. In FIG. 1, the LCD device includes an image display section 40, and a gate pad 42 and a data pad 44 connected between the driving ICs and the image display section 40. The image display section 40 has a structure in which a thin film transistor array substrate 48 and a color array substrate are attached to each other and has liquid cells arranged therein.
Within the image display section 40, the thin film transistor array substrate 48 includes data lines to which data signals are provided, gate lines to which gate signals are provided, a thin film transistor to switch the liquid crystal cells located at the intersection of data and gate lines, a pixel electrode connected to the thin film transistor to drive the liquid crystal cell, and a lower alignment film applied thereon to provide an alignment of liquid crystal materials.
The color filter array substrate 46 includes a color filter for producing colored light, a black matrix for prohibiting light leakage, a common electrode for producing a vertical electric field along with the pixel electrode, and an upper alignment film applied thereon for providing an alignment of liquid crystal materials.
The thin film transistor array substrate 48 and the color filter array substrate 46 are spaced from each other by a spacer in order to provide a uniform cell gap. In addition, liquid crystal material is filled into the cell gap provided by the spacer.
In FIG. 1, the gate pad 42 supplies gate signals from the gate driving IC to each gate line of the image display section 40. As shown in FIG. 2, the gate pad 42 includes a gate pad lower electrode 30 extending from the gate line and a gate pad upper electrode 32 connected to the gate pad lower electrode 30 via a gate contact hole 38 passing through a gate insulating film 12 and a passivation film 18.
In FIG. 1, the data pad 44 supplies data signals from the data driving IC to each data line of the image display section 40. As shown in FIG. 2, the data pad 44 includes a data pad lower electrode 34 extending from the data line and a data pad upper electrode 36 connected to the data pad lower electrode 34 via a data contact hole 28 passing through the passivation film 18.
Although not shown, the gate pad 42 and the data pad 44 are in contact with TCPs having the driving ICs mounted thereon in the TAB system. For example, the gate pad lower electrode 30 connected to the gate line is electrically connected to the gate TCP having the gate driving ICs mounted thereon via the gate pad upper electrode 32. Similarly, the data pad lower electrode 34 connected to the data line is electrically connected to the data TCP having the data driving ICs mounted thereon via the data pad upper electrode 36. Accordingly, the gate pad upper electrode 32 and the data pad upper electrode 36 serve to prevent the gate pad lower electrode 30 and the data pad lower electrode 34, respectively, from being damaged during repeated steps of contacting the TCPs that are required for the TAB system.
LCD devices (e.g., reflective-type LCD devices or In-Plane Switching-type LCD devices) do not require transparent conductive films. Similarly, transmissive-type LCD devices do not require transparent conductive films within the gate pad 42 and the data pad 44 in order to reduce a total number of mask processes and to lower manufacturing costs. Accordingly, these LCD devices have gate pads 42 and data pads 44, as shown in FIGS. 1 and 2.
FIG. 3A is a plan view of a pad structure according to the related art, and FIG. 3B is a cross sectional view along III1-III1′ of FIG. 3A according to the related art. Similarly, FIG. 3C is a plan view of another pad structure according to the related art, and FIG. 3D is a cross sectional view along III2-III2′ of FIG. 3C according to the related art. In FIGS. 3B and 3D, the gate pad lower electrode 30 and the data pad lower electrode 34 included in the gate pad 42 and the data pad 44, respectively, are entirely exposed.
FIG. 4A is a plan view of another pad structure according to the related art, and FIG. 4B is a cross sectional view along IV1-IV1′ of FIG. 4A according to the related art. Similarly, FIG. 4C is a plan view of another pad structure according to the related art, and FIG. 4D is a cross sectional view along IV2-IV2′ of FIG. 4C according to the related art. In FIGS. 4B and 4D, the gate pad lower electrode 30 and the data pad lower electrode 34 are partially exposed through a gate contact hole 28 and a data contact hole 38, as suggested in Japanese Laid-Open Patent Heisei 1-287624.
In the pad structures of FIGS. 3A-3D and 4A-4D the gate pad lower electrode 30 and the data pad lower electrode 34 are either completely or partially exposed to directly contact with the TCP having driving ICs mounted thereon in the TAB system. However, if a defect occurs due to misalignment caused when the TCP is bonded to the gate pad lower electrode 30 and the data pad lower electrode 34, repairing processes of attaching and detaching the TCP should be repeatedly performed several times. During the repairing processes, the exposed gate pad lower electrode 30 and the exposed data pad lower electrode 34 are both damaged by being pulled out together with the TCP. Accordingly, this damage causes electrical disconnection in both the gate pad lower electrode 30 and the data pad lower electrode 34.